Measuring urinary proteins is useful for diagnosing various diseases and symptoms. When these proteins are measured, they are highly diluted in buffer and then used. However, it is difficult to detect some proteins that have recently been attracting attention because of their low concentrations in urine, if these proteins are highly diluted in a conventional manner.
An example of a substance related to renal diseases is urinary megalin. Convenient means for testing renal disorders, which comprise measuring urinary megalin, are disclosed (Patent Documents 1 and 2).
Megalin also known as Glycoprotein 330 (gp330) or Low Density Lipoprotein (LDL)-receptor relate protein 2 (LRP2) is a glycoprotein having a molecular weight of about 600 kDa, which is expressed in renal proximal tubular epithelial cells (Non-patent Documents 1 and 2).
As a result of cell culture experiments using renal proximal tubular epithelial cells, the presence of two types of megalin, membrane-bound full length megalin and Soluble-Form megalin (fragment containing the extracellular region) lacking the intracellular region, is known (Non-patent Document 3). A method for measuring urinary full length human megalin, the extracellular region thereof, and the intracellular region thereof has also been reported (Patent Document 3).
Since urinary megalin concentration is low, high-degree dilution makes the measurement of urinary megalin difficult. Urinary megalin should be measured without high-degree dilution or measured with increased sensitivity. A measurement method not involving high-degree dilution is already known (Patent Document 4), but no method that involves increasing sensitivity exists. Development of a method for increasing sensitivity and the combined use thereof with the method of Patent Document 4 make it possible to detect urinary proteins with even lower concentrations. This leads to early disease detection and thus is advantageous in terms of medical economy.